The structure of the wall plate in chthamalus depressus (poli)

Abstract

The structure of the calcitic shell of extreme hypobiotic Chthamalus depressus (Poli) using untreated, treated, and polished material has been investigated by scanning electron microscopy, and supplemented by observations on normal forms and C. Stellatus (Poli). The laterale has been largely used. The plate is made up of prisms consisting of stacks of units ≈ 5 μm high; the prisms are separated by matrix and intraprismatic organic matter may also be present. The inner side of the plate is penetrated by holes. The structure of the wall plate is reflected in that of the sheath. Epicuticular lamina run across the wall plates separating the stacks of prisms. Attention is drawn to the possible implications with respect to the recent controversy regarding the form of chitin in crustacean endocuticle. The various structures give the surface a ‘banded’ appearance. From the available data on growth rate, shape, and moulting frequency, estimates are made of the expected size of these bands; the results agree reasonably well with the observations. The frequency of the smaller bands would seem to be endogenously determined by processes taking place within an intermoult period.